The present invention relates to a cylinder head gasket sandwiched between two engine members such as a cylinder head, a cylinder block and the like, of an engine for sealing.
In a state of the cylinder head gasket being sandwiched between a cylinder head and a cylinder block (cylinder body) of an automobile engine (internal combustion engine), the cylinder head gasket is tightened by head bolts to seal fluids such as combustion gas, oil, coolant water and the like.
Recently, as a method for reduction in weight of an engine, it has been progressed that an aluminum alloy is used as an engine material and an engine is made thinner, which causes lower rigidity of the engine. Accordingly, in view of the condition of sealing of a recent head gasket for a multi-cylinder engine, there has been a tendency of increasing a failure of local leaking of combustion gas. The major factors are increases of a local lower rigidity of an engine and an unbalanced temperature distribution.
Especially, with the lower rigidity of the engine, an amount of tightening force is restricted when the gasket is tightened. Accordingly, sealing surface pressure tends to become lower around a combustion chamber (cylinder bore). As a measure for the decrease of a sealing surface pressure, in order to reinforce the surface pressure, an entire surface pressure is increased at a sealing portion around a combustion chamber, and a material of a bead is changed to a material having spring action. Also, a method using a reinforce plate such as a shim has been commonly employed.
As one of the measures, in a metal gasket provided with a seal bead around the combustion chamber for increasing the surface pressure, a metal gasket has been provided with a slit for decreasing a rigidity of the seal bead outside the seal bead around the combustion chamber except a space between the adjacent combustion chambers to thereby enhance a tightening ability between the adjacent combustion chambers (for example, refer to Japanese Patent Publication No. TOKKAI 2001-132843).
In the metal gasket, since the tightening force becomes insufficient between the combustion chambers by the rigidity of the seal bead around the combustion chamber except the space between the combustion chambers, the bead rigidity of the seal bead is partially adjusted by the slit to thereby improve the tightening ability.
On the other hand, the cylinder head gasket has portions contributing to sealing such as the seal bead and like around the combustion chamber, a water hole, a fluid hole, a bolt hole and the like, and the other portions except the portion described above. The tightening forces by the tightening bolts are mainly applied to the portion contributing to sealing, but also applied to the other portions. Surface pressures are low at the other portions, and parts of clamp forces do not directly contribute to sealing since the dimensions are relatively large. Thus, there is a problem that the clamp load for sealing can not be sufficiently used for sealing.
Also, with the lower rigidity of the engine, the cylinder head is distorted to concave downward at a longitudinal center portion of a joint surface for a grommet and a bead of the combustion chamber hole. Accordingly, there is a problem of being deteriorated in a sealing ability between the joint surfaces.
As a measure for the problem, a metal gasket has been provided with projections having capabilities of a heat resistance, an incompressibility, and a non-deforming ability, at both ends in a longitudinal direction of the gasket. When the tightening bolts are tightened, a space between the cylinder head and the cylinder block does not become narrow at the both ends in the longitudinal direction of the engine. Therefore, the joint surface of the cylinder head is not distorted to concave downward at the longitudinal center portion to thereby prevent curving (for example, refer to Japanese Patent Publication No. TOKKAI H09-292027).
The projection is formed with a fluid coating material such as an epoxy resin or the like by a screen printing and a filling of a hard synthetic resin layer such as the epoxy resin in an inner space of an emboss bead integrally provided in a metal plate. Therefore, there is a problem of slightly increasing the weight of the projection to thereby increase the coating process of the epoxy resin.
The present invention is provided to solve the problems described above. An object of the present invention is to provide a cylinder head gasket provided with a notch portion for reducing surface pressure to thereby reduce the surface pressure at the portion which does not directly contribute to the sealing surface pressure. Therefore, the clamp load of the reduced surface pressure is used for the sealing surface pressure to thereby increase the sealing surface pressure around the combustion chamber. Accordingly, an excellent sealing ability can be obtained.
Further objects and advantages of the invention will be apparent from the following description of the invention.